Field of the Invention
The invention relates to an integrated circuit fabrication, and particularly relates to a method of forming a semiconductor device.
Description of Related Art
Generally, a memory device includes a select gate and a control gate, and an oxide-nitride-oxide (ONO) layer serves as a control gate insulating layer and also serves as a charge storage layer for memory and an oxide layer serves as a select gate insulating layer. In the conventional method of forming the control gate insulating layer, a sacrificial oxide layer is formed over a substrate including a select gate area and a control gate area, and then by using a hard mask layer exposing the control gate area and covering the select gate area, the sacrificial oxide layer in the control gate area is removed. Thereafter, an ONO layer is formed in the select gate area and the control gate area, and the ONO layer and the hard mask layer therebeneath in the select gate area are removed. Accordingly, the remained ONO layer in the control gate area forms the gate insulating layer for the control gate to be formed.
However, when using a silicon nitride layer as the hard mask layer, the ONO layer and the hard mask layer therebeneath at the boundary of the select gate area and the control gate area are difficult to remove completely since the ONO layer has a steep sidewall. As a result, as shown in FIG. 1, the ONO residue R is remained between the select gate SG and the control gate CG. Furthermore, when performing an implantation process on the substrate by using the select gate and the control gate as a mask, a good implant profile is hard to achieve due to the masking defect of the ONO residue, and the electronic performance of the device may be effected.